Sealing compositions are pumped to fill the gap occurring between tail brushes on the inside of the shield, to seal them and avoid ground water, grout or contaminants in general to enter.
They shall have excellent resistance against:                water wash-out        mechanical wear and pressure        flowing-off/extrusion        
At the same time they have to show important features as:                strong adhesive properties        high stability without fluid separation        low toxicity and environmental compatibility        
To further enhance their environmental compatibility, it is also highly desirable to have hydrocarbon free sealing compositions.
Known tail seals are usually made of a hydrophobic portion, a mineral charge, fibrous material and various additives and are in the form of sticky pastes.
Their maximum consistency is limited by the capacity of the pumping devices, that usually work by pressing out the mixture from its container.
The hydrophobic portion is responsible for adhesion to the metallic surface, for insulation from water leakage and its chemical structure strongly influences the rheology of the sealant.
To adequately perform its role, the hydrophobic portion normally represents at least 30% of the sealing composition.
The mineral charge is used as filler, its maximum concentration being limited by the maximum final viscosity and consistency of the composition.
The fibrous materials are usually added in small percentages (1 to 10% by weight) to improve the pastiness and lubricating characteristics of the sealing composition.
Additives can be chosen among emulsifiers, gelling agents, viscosifiers, preservatives, corrosion inhibitors added alone or in combination.
Among the patents concerning specific compositions useful as tail seals we cite:                U.S. Pat. No. 5,478,385, describing sealing compositions comprising a hydrophobic portion, a lipophilic emulsifier and at least 20% water, in sufficient concentration to inhibit combustion of the composition;        FR 2 807 058, concerning a water reactive emergency sealing composition comprising a gelling or thickening agent;        JP 09-208943, describing seal tails that contain a synthetic pour point depressant, up to 60 wt % mineral charge and a biodegradable oil or grease or mixture thereof; in this publication, blown oil are not mentioned among the utilizable oils and greases and, although mineral charges like inorganic carbonate or sulfate are cited, in the examples desirable high levels of mineral charge are only obtained by using inorganic materials in the form of paste or talc (normally talc is commercially available with relatively small mean particle size, between 1.5 and 37 microns and possesses lubricant properties).        